Shocks/dampers to reduce wheel hop
Turbo Mini Forums

I'm putting a lot of power through the front wheels and am experiencing problems with wheel hop on hard launches and powering out of corners, the current set-up is standard rubber cones (only a year or so old genuine ones), gaz dampers and yoko a032r tyres (suspension geometry and cornerweights all spot on) . I want to keep the ride reasonable as its mainly a road car with occasional track days and 1/4 mile action. I've read up loads about dampers but there isn't much about reducing wheel hop apart from a brief mention in one of keith dodd's articles where he say some special koni twin tube dampers where the only ones that cured wheel hop on his 8 port. Has anyone experienced wheel hop with a powerful mini and found a damper that reduces it?

What diff are you running?

I assume the rest of the suspension is polybushed and not rubber? And is the front subframe solid mounted?

GAZ dampers are ok, but it seems that they may not be correctly valved for your setup.

Have you tried experimenting with tyre pressures?

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

It's a torsen diff (k series with rover pg1 gearbox). subframe is sold mounted and bushes are poly/up-rated. Up to around 130bhp it would probably be fine its putting 180bhp + though the front wheels and i'm pretty sure the dampers are struggling, i know the Gaz are the bottom end of the range, so i'm happy to improve these anyway

Edited by gazwad on 1st Aug, 2017.

What he said. You can do the chalk test method to get the proper pressure for your tires.

stiffer engine mounts help a lot, cant remember what your running? but the dampers are most likely the cause as they just wont be strong enough.

Assuming none if your pollybushings have crushed up and became baggy.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

bushes are all good. the engine mounts are fairly solid too with an extra gearbox steady. there's nothing wrong with it and it only does it when using all of the power (i have to feather the throttle to reduce it). I 100% sure the dampers are not up to the job, just want some recommendations from people who might have had the same problem, what dampers do you use denis?

Edited by gazwad on 1st Aug, 2017.

standard ones and ancient rubber cones.i just lift when I get wheelhop and roll back into it. its never an issue on normal road tyres or slicks, only trackday tyres. so absolutely no help to you :(

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

Chalk test?

So it's a K-series with 180 bhp! excellent.

Is it on 10" whwwls (I assume it is as it's on AR32s).

Do you run an ARB?

I'm not sure what damper I would advise as I couldn't guarantee to solve the problem.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

yep it's on 10" cooper s steel wheels, i have a rear arb but not on the front

I wonder if a front ARB might help. Obviously it will affect other handling characteristics.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

I'm also thinking ARB would be an ideal thing to try after corner weights.

what front geo settings ?

is it possible the bulkhead is flexing ,maybe try it with the bonnet front end off to see whats moving ?

what tyre pressures ?

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

interesting ive herd of this with rwd nd leaf springs but not on fwd

anyone use the spax or protech brand?

Lots of my FWD cars have had wheel hop, my old 1.1 fiesta was terrible, even my 2013 diesel Mondeo does it if you do an emergency start in certain conditions.

As for SPAX and Protec...........

The guy who was 'Mr SPAX' and responsible for them being great dampers, sold the company and started GAZ, then he sold that and is now 'Mr Protech'. Well that's what I have been told.

If I was buying new dampers for the hillclimber I'd buy the twin-adjustable protechs. I presume he has enough data to build suitably valved ones for a mini on doughnuts.

Edited by wil_h on 3rd Aug, 2017.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Both my current and previous daily wheel hop like mad in the wet when the front wheels load up, I just assumed it's a fwd and firm suspension thing.

+1 for protechs, best dampers I've had on the mini so far.

I have worked on and simulated drivetrain issues which have fallen in to this category, it's not my field but I have a layman's understanding of it....

Sorry this is so long... genuine wheel hop, (wheel hop resonance) isn't a simple mechanism to describe

The traction limited, grip - slip 'wheel hop' that you mention is typically a driveline 'windup' problem:

In this instance on a hard launch initially the tyre/s grip, the drivetrain 'winds up' and as a result of the torque reaction the engine / gearbox all shift on their mounts....

Then the tyres suddenly lose grip and all of the drivetrain unloads and as it is essentially undamped and all of this driveline energy is released...

Then if you keep your foot in the tyre continues to grip / slip and the drivetrain continues to bounce back and forth...

The natural frequency of an engine / gearbox on it's mounts is typically in the 10 - 13 Hz range

'Wheel hop' natural frequency is a function of the axle mass versus the suspension spring rate and tyre rate and also typically falls in the same 10 - 13Hz range.

Because the engine / gearbox provides a 'forcing' frequency which is so similar to the wheel hop natural frequency we get resonant wheel hop.

As Denis mentioned lifting off solves the problem as it removes the tyre grip / slip mode and hence the initial cause is removed, but not always practical or desirable.

The mechanisms for tyre grip / slip are complicated and numerous road conditions (wet, damp, dry, uneven) / car setups can cause it, but just to be clear not all loss of traction causes grip / slip.

So it's easy to see why so many people will have different opinions on the causes and hence solutions to the problem, as an example if someone fits an LSD and this causes a grip / slip scenario and he hails that all LSD's cause wheel hop.

So we have 3 stages:

1.) Traction limited tyre grip / slip which causes the initial 'excitation' to the drivetrain.

2.) The drivetrain oscillates at it's natural frequency forced by the tyre grip / slip.

3.) The wheel hop resonance is forced by the drivetrain oscillations. Which feels like your car is trying to smash itself to bits, because it is.

In my opinion the ideal solution is to try and stop stage 1.) the initial grip / slip behaviour but this will have to be trial and error, it could be a chronic problem and no amount of setup changes stop it or you could stumble on something quickly, try the cheap / no cost stuff first, tyre pressures up / down, borrow another set of front wheels / tyres, does it happen with a passenger as well? This will give you some idea how likely you are to fix the grip / slip, does it change at all?

Dampers often fall in to the old / worn out / not replaced frequently enough category and if damping is way below where it should be then what is called excessive contact patch load variation can occur which can and does easily aggravate grip / slip, can you borrow even a standard pair of new / newish dampers? As this is where I'd start, not necessarily stiffer, just different to what you have.

As far as fixing stage 2.) Denis mentioned stiffer engine mounts and this is a very common fix for resonant wheel hop, it works because stiffer engine mounts cause the natural frequency of the drivetrain to move higher and above where the wheel hop natural frequency occurs and as a result the drivetrain doesn't excite the wheel hop, the downside being that engine vibrations are likely to be worse and refinement suffers. Try and fit spacers or shims to prevent / reduce engine movement and see if this helps / fixes the problem as a cheap test? Competition / drag cars do this as it has the added benefit that everything moving less helps with gear changes.

Stage 3.) IMHO by far the worst thing to try and fix, generally the increase in damping level required is way above what is needed for normal wheel control and will ideally necessitate measuring the dampers you have and using this as a start level for adjustable dampers, don't get hung up on having bump and rebound seperately adjustable, single bump / compression adjustable dampers almost always stiffen the rebound damping as well as it is difficult to effectively separate the two with the method of adjustment they use such as bleed / bypass variation.

Fixing the grip / slip means you don't introduce harshness from stiffer engine / trans mounts required in stage 2 and you don't have the unduly harsh damping required in stage 3, also just trying to fix stage 3 'wheel hop resonance' means that your drivetrain is still trying to smash itself to bits.

Still awake

Cheers

Edited by Aubrey_Boy on 4th Aug, 2017.

Most excellent, really useful explaination.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Thanks for that, very informative! I know my gaz dampers are past their best as they are starting to rattle on rough roads (and i dont think they are very good from new anyway - a suspension guru once described them to me as 'happy shopper dampers'). I chucked some (very) old koni's on that I had in the back of the shed and it has significantly reduced the hop as well as improving the ride as well, so this seems to prove its a damper problem. I won't keep the koni's on though as they can't be adjusted on the car and I like to be able to play at the track side. Just got to decide between Avo or protech, avo are local to me which is handy, but protech seem to be highly rated by most...

Edited by gazwad on 7th Aug, 2017.

Don't discount AVO, decent dampers.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Koni 'motorsport' adjustable 'coilovers' / dampers are very good, I've used them for years on a variety of cars, I have a bit of experience with the insanely expensive FIA Historic units they sell through Swiftune but a good few of the front running cars use them.

Protech are very helpful and my dealings with Kevin have been good, he was willing to create dampers with the force / velocity curves I specified for my inboard coilovers for my Mini and I'll do the same for my inclined rears. But I can't see why their off the shelf Mini specific units wouldn't suit your needs assuming your car isn't much heavier than an A series car? Say 200kg ish per front corner? Quite a few cars on here are about that weight or less I think

I have no experience with AVO but I'd go with Protechs 400 series which is a single adjustable for both bump and rebound and gives a pretty good range of adjustment, I dynoed the units he sent me and found they were a very closely matched pair, easily within one click of each other.

I decided to go with protechs as everyone i have spoken to has recommended them. Will update as to the results when they are fitted